The present invention generally relates to magnetic tape drives. More specifically, the invention relates to magnetic tape drives for tape cartridges housing quarter-inch (1/4 inch) width magnetic tape, e.g., streaming tapes for microcomputers.
Streaming magnetic tape drives generally are known wherein data are recorded on/played back (or read) from a length of magnetic tape contained in a streaming tape cartridge or cassette. Such cartridges essentially are rectangular and generally have a length greater than a width. Further, the cartridge includes not only the magnetic tape, but a capstan idler, a hinged dust cover, as well as a metal base plate.
An operator generally pushes the cartridge or cassette into an insertion channel toward a magnetic read head. Depending on the drive, the cartridge is inserted either width wise, i.e., front loaded, or length wise, i.e., end loaded.
Streaming tape cartridges including quarter inch (1/4 inch) width magnetic tape usually come in two formats. One format generally is referred to as the 3-1/2 inch form factor. The other format generally is referred to as the 5-1/4 inch form factor.
For example, for many years tape drives have been available for providing back-up storage for personal computers having Winchester disk drives. They permit the entire contents of the hard disk to be stored on a single tape cartridge of, for example, the type defined by ANSI X3.55-1977. See also U.S. Pat. No. 3,692,255, incorporated herein by reference. This type of cartridge has been sold in large numbers under the designations DC300 and DC600 by Minnesota Mining and Manufacturing Company.
Both the DC300 and the DC600 are identical mechanically except for the length of tape. This type of tape cartridge is hereafter referred to as the "DC600-type" cartridge, which is presently the most widely used configuration. That cartridge measures six inches in length by four inches in width. It has a belt capstan roller which may be engaged by a capstan drive roller to propel a length of magnetic tape, either 300 feet or 600 feet, between a pair of reels inside a plastic housing. The cartridge further has a hinged tape access door which may be opened to expose the tape. The opening of this tape access door increases the width of the tape cartridge from four inches to five and three-quarter inches when the door is fully opened. Both the DC300 and the DC600 are identical mechanically except for the length of tape.
For many years both floppy disk drives and Winchester disk drives have been manufactured according to a de facto size standard which requires that they fit within a physical envelope (rectangular box) measuring three and one-quarter inches in height by give and three-quarter inches in width by eight inches in length. The aforementioned dimensions are known throughout the computer peripherals industry as the five and one-quarter inch form factor. This is a name derived from the diameter of the disk.
Originally the DC600 type cartridge was designed to be loaded sideways into a tape transport sized to fit an earlier, larger form factor measuring eight inches in width. When the five and one-quarter inch Winchester disks first became popular it was believed that a tape drive could not be provided that would permit endwise loading of the DC600-type tape cartridge into the same form factor. The term "endwise" refers to loading the cartridge so that the side edge with the tape access door and belt capstan roller is generally parallel to a longitudinal axis of the frame (eight inch dimension of the form factor).
A variety of tape drives and tape cartridges are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. Title ______________________________________ 5,025,334 Auto-Loading Transport For Tape Cartridge With Tape Access Door And Belt Capstan Roller 4,807,067 Cartridge Tape Drive Re. 33,224 Drive For End Loading And Transversely Shifting Tape Cartridge 4,673,995 Cartridge Tape Drive With Friction Roller To Open Cartridge Door 4,337,908 Cartridge-Loading Apparatus For Tape Recorder Drives 4,785,363 Cartridge Alignment Mechanism For Tape Drive 4,636,890 Magnetic Tape Recorder 4,514,775 Streaming Cassette Tape Transport 4,656,541 Front Loading Cartridge Activated Clamp And Eject Mechanism 4,156,260 Cartridge-Loading Tape Recorder 3,964,098 Tape Deck With Drive Motor Remote From Driver Roller 4,573,091 Cartridge Tape Drive 4,556,923 Tape Cartridge Drive With Cartridge Door Opening Mechanism 4,498,112 Tape Cartridge Receptacle ______________________________________
The disclosures of these patents are fully incorporated herein by reference.
The 3-1/2 and 5-1/4 inch form factor magnetic tape cartridges generally are rugged and enjoy a relatively high reliability in use. However, due to the presence of the metal base plate, an electrostatic discharge can occur between the cartridge and the drive chassis when the cartridge is inserted into the drive. The discharge can occur because the metal base plate provides a low impedance source of charge.
Transient currents that result from these discharges can occur rapidly and have rise times in the nanosecond range, as well as magnitudes in the ampere range, if the discharge occurs between the base plate and drive chassis ground.
Streaming tape drives generally include a data bus by means of which data is communicated to and from electronics associated with the tape drive and, for example, a computer system. Due to the very low impedance of the data bus ground connected to the tape drives, and the unpredictable and sometimes high impedance between the tape drive casting and the computer chassis, transient waveforms arising from the transient-currents will partly couple into the data bus ground path and signal wires and disrupt data signalling. When this happens, errors fatal to operation of the computer system may occur.
In U.S. Pat. No. 4,847,711 there is described an electrostatic charge grounding system for an audio tape cassette drive. In this system, electrostatic charge on a cassette or disk is grounded, when the latter is inserted into a drive therefor through an opening formed in a front panel of the drive, through a grounding path connecting a hinge pin of a flap covering the opening normally by a biasing spring associated therewith to a chassis of the drive. There is, however, no provision for grounding the base plate of a streaming tape cartridge or for preventing data bus signaling disruptions.